let bool := Prop,
    and := λ p q, Π c, (p → q → c) → c,
    and_intro := λ p q H1 H2 c H, H H1 H2
in and_intro :
  ∀ p q,
    p → q → (∀ c, (p → q → c) → c)
let1.lean:19:19: error: type mismatch at term
  λ p q H1 H2 c H,
    H H1 H2
has type
  ∀ p q,
    p → q → (∀ c, (p → q → c) → c)
but is expected to have type
  ∀ p q,
    p → q → (λ p q, ∀ c, (p → q → c) → c) q p